The invention relates to an installation for determining the temperature of the heater coil of an x-ray tube.
X-ray tubes are employed in x-ray diagnostics for fluoroscopy or radiography. In the case of some examination techniques, one must be able to rapidly alternate from fluoroscopy to radiography. Radiography is only then possible when some control functions are executed. One of these necessary control functions is, after selection of the heater coil of the x-ray tube necessary for radiography, the production of a high emission temperature of this coil.
If a switch-over is effected from fluoroscopy to radiography, the following occurs, among other things: The fluoroscopy x-ray tube voltage is disconnected (or switched off). The coil which, corresponding to the low fluoroscopy x-ray tube current, was only somewhat heated, is heated to the radiography temperature. As soon as it has assumed this temperature, the radiography x-ray tube voltage is permitted to be connected.
In the case of x-ray tubes comprising two heater coils, during the changeover from fluoroscopy to radiography, also the coil can be changed. Here, the radiography coil must then be heated from a temperature, at which it just barely did not yet emit, to radiography temperature. This operation lasts up to one second and can determine the transition time between fluoroscopy and radiography. It lasts particularly long when the filament power, with which electronic heating is effected, is not substantially greater than the filament power, with which the emission temperature is maintained.
Thus, in the interest of a short transition time from fluoroscopy operation to radiography operation, it is of importance to supply increased power to the coil for a time interval until it has the desired radiography temperature.
In the interest of a short transition time from radiography operation to fluoroscopy operation, it is analogously of importance to supply no power to the coil for a time interval until it has the desired fluoroscopy temperature.
The increased power or the heating pause can be allocated to the coil by a controlled heating circuit or by a closed loop regulated heating circuit.
A controlled (open loop) heating circuit can be improved if one measures the coil temperature and utilizes it as a dimensioning quantity.
In contrast to a controlled heating circuit, a closed loop regulated heating circuit, by definition, has an actual value determination (or detection). Such a regulated heating circuit would supply to the coil increased filament power for a length of time until the determined actual value, which reproduces the heating coil temperature, has attained a desired setpoint value which a memory in the heating circuit supplies when addressed with the radiography parameters: x-ray tube current and x-ray tube voltage.
Conversely, a closed loop regulated heating circuit would not supply any filament power to the coil in the transition time from photography to fluoroscopy for such a length of time until the actual value, which represents the heating coil temperature, has attained the desired value, which the memory communicates (or signals) as necessary for the fluoroscopy operation.